This invention pertains to the packaging of certain products, and particularly to multiple layer packaging films used for forming heat sealable packages. The invention specifically addresses packaging applications in which closure seals are strong, and particularly those in which the product is sentive to infusion of air, or the like, into the package through the seals which are formed during package closure.
In the design of flexible packaging films and the packages formed from them, the artisan deals with the dual objective of providing strong package closure in combination with ease of opening of the package to gain access to the product contained therein. Various package designs are available for opening the packages so formed. These often take the form of weakness lines, scores, cuts, perforations and the like. Many of such designs require a separate operation on either the film or the package to ensure proper opening of the packages. Some may also penetrate the package itself, thus violating any gas barrier property of the film. Separate operations, of course, have a cost and impute an economic penalty to the films so made.
A highly desirable and economical method of providing for opening of the package is by making the closure seals such that they can be pulled apart. While the peelable seal is highly desirable in that it is economical to manufacture and easy to use, packages having peelable seals have not heretofore offered, in combination, the properties of hermetic, or gas-tight, seals, or inseparable seals.
In the packaging of products that are sensitive to certain gases in the air, it is imperative that the infusion of the gases be prevented. Gas barrier properties of various of the commercially available polymers commonly used in packaging films are known. These gas barrier properties are useful for preventing gaseous infusion into a package through the packaging film. There is still, however, some possibility of gaseous infusion through the seal area of the package, such as through heat seals which may be about the periphery of, for example, a pouch, where the seals do not provide an impervious barrier, whether by chemical composition or physical assemblage.
While the polymers commonly used to form heat seals are not normally considered as particularly good gas barriers, they may function as such by virtue of the thickness of the seal, from inside the package to its exterior taken through the seal, if a physically gas-tight seal is made, normally an hermetic seal, which property is usually associated with an inseparable seal.
In the formation of heat seals, two polymer layers, typically of identical composition, are brought together with heat and pressure, such that the layers are softened and somewhat fused together. To the extent softening and fusing is accomplished, the seal strength is enhanced. Seal strength is also enhanced by the homogeneity and internal cohesiveness of the layers so sealed.
It is known that inseparable seals may be formed by polymers that exhibit good softening and fusing properties. A polymer such as surlyn ionomer, for example may form inseparable heat seals and provide an hermetically sealed, gas-tight package. In a well-formed surlyn seal, the interface between the two layers so sealed essentially disappears, such that the surlyn layers in the seal area appear to function as a single layer joining the two films which form the sides of the package.
While such a strong seal is highly desirable in that it provides excellent package integrity at the seals and typically prevents gaseous infusion through the seals, a package so well sealed as this may be difficult to open. Indeed, the ultimate intent is the opening of the package and use of the contained product. While access to the package may be achieved such as by special package mechanical design, or by a sharp tool, it would be highly desirable to simply peel the package open. Because hermetically sealed packages normally have inseparable seals, hermetically sealed packages have not heretofore been available with peelable opening features to gain access to the package contents.
It is a general object of this invention to provide a package having strong seals in combination with a ply-separating peel capability and good oxygen and moisture barriers.
It is a more specific object of this invention to provide an hermetically sealed package which can be readily peeled open.
It is further object to provide, in such a package, film layers which offer excellent barrier to transmission of particularly, oxygen and water vapors.
It is yet another object to provide a method of opening a sealed package, to expose the contents, where the seals of the facing, innermost, layers of the sealed package are not conducive to ply separation.
It is still another object to provide, in a package made from a multiple layer film, package closure by means of inseparable heat seals, in combination with package opening by a partial tearing through of the packaging film and ply separation.